The present invention relates to electrostatographic reproduction machines, and more particularly to such a machine including a pneumatically coupled sonic toner release development apparatus for improving reliability, as well as uniformity of non-interactive development acoustic motions, and of the resulting toner development.
The present invention can be utilized in the art of xerography or in the printing arts. In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on an image bearing surface of a uniformly charged photoreceptor. The charge on the surface is selectively dissipated in accordance with an image-wise pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent pattern of charged and discharged or charge dissipated areas on the imaging surface. In what is referred to as a Charged Area Development (CAD) environment, the discharged or charge dissipated areas on the photoreceptor correspond to residual or background voltage levels, and the still charged areas correspond to image areas. In what is referred to as a Discharged Area Development (DAD) environment, the discharged or charge dissipated areas on the photoreceptor correspond to residual or background voltage levels, and the discharged areas correspond to image areas.
In either environment, the image areas are then developed or rendered visible with charged toner particles. The charged toner particles generally comprise a colored powder whose particles adhere to the charge pattern on the image bearing surface, thus forming a toner developed image. The toner developed image is then first transferred to a receiving substrate, such as plain paper, to which it is then heated and fixed by any suitable fusing technique.
Conventional xerographic imaging techniques which were initially limited to monochrome image formation have been extended to the creation of color images, including process as well as highlight multicolor images. In either case, particularly in single pass multicolor image process machines and highlight color machines, toner developed images from an upstream development unit of the machine must be moved through the development fields of a downstream development unit. Scavenging or undesirable removal of some of the toner particles from the previously developed image, usually resulting in a less than desired quality final image, is ordinarily a problem in such multicolor machines.
Pneumatically coupled sonic toner release development techniques and apparatus have been proposed for use in such multicolor image machines in order to reduce such scavenging, as well as, interaction between the previously developed image and the downstream development fields, in order to improve the developed image quality. Such donor-development or pneumatically coupled sonic toner release development techniques include conventional prior art development electrode types, for example, the exposed development electrode wire technique, and the embedded development electrode techniques, examples of which will be described below. Such pneumatically coupled sonic toner release development techniques also include conventional vibratory or electrostatic techniques, for example, that using sonic toner release, that using a piezo-active donor roll, and that using an electrostatic transducer, examples of which will also be described below.
Following then is a discussion of examples of such prior art, incorporated herein by reference, which may bear on the patentability of the present invention. In addition to possibly having some relevance to the question of patentability, these references, together with the detailed description to follow, may provide a better understanding and appreciation of the present invention.
U.S. Pat. No. 5,523,827 entitled Piezo Active Donor Roll (PAR) For Store Development, issued Jun. 4, 1996, to Snelling et al., discloses a vibratory type development system which uses a donor roll structure including a piezoelectric layer for liberating toner particles from its surface. The donor roll is provided with a plurality of electrodes spaced about the circumference of the roll. An AC voltage is applied to the electrodes as they pass through a developer nip or zone intermediate the donor roll and an imaging member containing latent electrostatic images. The voltage is applied to each electrode and another continuous electrode which together sandwich the piezoelectric layer therebetween such that an AC voltage is applied across a portion of the piezoelectric layer in the nip thereby causing electrostatic excitation of the portion of the layer only in the nip.
U.S. Pat. No. 5,339,142 entitled AC/DC Spatially Programmable Donor Roll For Xerographic Development and issued Aug. 16, 1994, to Hays, discloses a development electrode type non-interactive development system for use in color imaging. To control the developability of lines and the degree of interaction between the toner and receiver, an AC voltage is applied between a donor roll and electrodes supported adjacent to the surface of the donor roll to enable efficient detachment of toner from the donor to form a toner cloud. An AC voltage applied between the donor assembly and an image receiver serves to position the cloud in close proximity to the image receiver for optimum development of lines and solid areas without scavenging a previously toned image.
U.S. Pat. No. 4,546,722 granted on Oct. 15, 1985, to Toda et al discloses a vibratory or electrostatic type development apparatus having a toner carrying member and a piezoelectric vibrator for displacing toner from the toner carrying member and causing it to fly in a manner to avoid depositing toner onto a non-image area of an image bearing surface. Such an arrangement prevents degradation of the charged image for the purpose of image preservation. Toner release control and adverse, image degradation influences are still likely, given the magnitude of the electrostatic fields.
U.S. Pat. No. 4,987,456 granted to Snelling et al., on Jan. 22, 1991, is directed to a conventional vibratory or electrostatic type apparatus in which a resonator suitable for generating vibratory energy is arranged in line mechanical contact with the back side of a charge retentive member bearing an image on a surface thereof, in an electrophotographic device, to uniformly apply vibratory energy to the charge retentive member. The resonator comprises a vacuum producing element, a vibrating member, and a seal arrangement. Where the vibratory energy is to be applied to the charge retentive surface, a vacuum is applied by the vacuum producing element to draw the surface into intimate engagement with the vibrating member, and edge seal arrangement. The invention has application to a transfer station for enhancing electrostatic transfer of toner from the charge retentive surface to a copy sheet, and to a cleaning station, where mechanical vibration of the surface will improve the release of residual toner remaining after transfer.
U.S. Pat. No. 5,255,059 granted on Oct. 19, 1993, to Kai et al., discloses a vibratory or electrostatic type image forming apparatus incorporating a stationary, hollow cylindrical donor structure including a single set of electrodes within its hollow, and a piezoelectric layer formed over the electrodes. The donor structure may be in the form of a roll or a belt. In each embodiment disclosed, a phase shifted voltage is applied to the electrodes for the purpose of creating a waving action which is effective to transport toner particles from a sump to a development zone. Thus, while the toner is moved through electrostatic action alone of the waving materials, the donor structure itself is stationary.
U.S. Pat. No. 4,568,955 issued on Feb. 4, 1986, to Hosoya et al., discloses a development electrode type recording apparatus wherein a visible image based on image information is formed on an ordinary sheet by a developer. The recording apparatus comprises a donor roller spaced at a predetermined distance from and facing the ordinary sheet and carrying the developer thereon, a recording electrode and a signal source connected thereto for propelling the developer on the developing roller to the ordinary sheet by generating an electric field between the ordinary sheet and the developing roller according to the image information, and a plurality of mutually insulated electrodes provided on the developing roller and extending therefrom in one direction. An AC and a DC source are connected to the electrodes, for generating an alternating electric field between adjacent ones of the electrodes to alone cause oscillations of the developer found between the adjacent electrodes along electric lines of force therebetween to thereby liberate the developer from the developing roller, and to thereby form the toner particles into smoke in the vicinity of the donor roller and the sheet.
U.S. Pat. No. 5,010,367 granted to Hays on Apr. 23, 1991, relates to a development electrode type non-interactive development system for use in color imaging. To control the developability of lines and the degree of interaction between the toner and receiver, an AC voltage alone is applied between a donor roll and electrodes supported adjacent to the surface of the donor roll to enable detachment of toner from the donor to form a toner cloud. An AC voltage applied between the donor assembly and an image receiver serves to position the cloud in close proximity to the image receiver for optimum development of lines and solid areas without scavenging a previously toned image.
U.S. Pat. No. 4,833,503 granted to Snelling on May 23, 1989, is directed to a multi-color printer using a conventional vibratory or electrostatic type apparatus. In it, vibratory energy only is provided by a sonic toner release development system in an attempt to develop either partial or full color images with minimal degradation by subsequent over-development.
U.S. Pat. No. 4,647,179 issued Mar. 3, 1987, to Schmidlin, discloses a development electrode type development apparatus including only a traveling electrostatic AC wave conveyor for transporting toner particles from a development housing to an imaging surface. The traveling electrostatic AC wave conveyor comprises a linear array of spaced apart conductive electrodes and a phase shifted multiphase AC voltage source connected to the electrodes for creating the wave.
U.S. Pat. No. 4,868,600 issued Sep. 19, 1989, to Wayman et al., discloses a development electrode type development apparatus in which AC electric fields alone are applied to self-spaced electrodes positioned within a development nip. The electrodes are mounted at their ends to bearing blocks, and are self-spaced from the donor member by toner particles.
Non-interactive vibratory or electrostatic type development units, (as disclosed in any of the relevant example references above), typically each utilizes vibratory energy alone to effect toner particle release from the development nip side of the donor member by mechanically reducing toner particle adhesion forces on the donor member. The vibratory energy alone therefore must be of a level high enough to effect such toner release, and additionally enable toner particle travel for image development across an air gap in the development nip within a D. C. electrostatic field. A lack of uniformity of vibratory motion in the development nip necessary over the full length of the donor roll to accelerate the toner particles to release from the donor member is an issue for these devices.
Nonetheless, Sonic toner release (STORE) development, as disclosed for example in U.S. Pat. No. 4,833,503 (cited above), advantageously occurs advantageously at electric field magnitudes well below those at which air breakdown and other image noise generation effects occur. However, such (STORE) development has so far depended primarily upon application of either piezoelectric polymer film donors or passive donors acoustically activated by mechanical coupling to the tip of an acoustic waveguide. Thus the primary approach has been mechanical coupling of acoustic waveguides to passive donor members.
Unfortunately, development uniformity as pointed out above is an issue in such development processes due to use of mechanical coupling. This is because the operating space for the development process is near to the threshold for toner release from the donor. Acoustic Transfer Assist (ATA) toner release development, on the other hand, operates at relatively high values of electric field which undesirably tend to reduce sensitivity of the (ATA) process to non-uniformities in the magnitude of acoustic motions. Non-uniformities and variations in mechanical coupling between waveguide tip and donor member surface are believed to occur due to wear, dirt and debris build up, and non-uniformities in tension holding the donor member in contact with the waveguide tips. Additionally, mechanical coupling also results in non-uniformities due to inherent waveguide tip motions.